Question

#include "stdafx.h"
#include <exception>

template<class T>
class NoCheck;

template<class T>
class EnforceNotNull
{
public:
    //EnforceNotNull(const NoCheck<T>&){}//<<-----If this is uncommented it works
    static void Check(T* p)
    {
        class NullPtrException : public std::exception
        {
        };

        if (!p)
        {
            throw NullPtrException();
        }
    }
};

template<class T>
class NoCheck
{
public:
    NoCheck(){}
    NoCheck(const NoCheck&){}
    NoCheck(const EnforceNotNull<T>&){}
    operator EnforceNotNull<T>() {return EnforceNotNull<T>();}//<<-----This seams to not do its job
    static void Check(T* p)
    {/*Empty body*/}
};


template<class T, template<class> class CheckingPolicy>
class SmartPtr : public CheckingPolicy<T>
{
public:
    SmartPtr(T* p)
    {
        Check(p);
    }

    template<class T1, template <class> class CheckingPolicy1>
    SmartPtr(const SmartPtr<T1,CheckingPolicy1>& pattern):pointee_(pattern.pointee_),
        CheckingPolicy<T>(pattern)
    {
    }
    T* pointee_;
private:

};

int _tmain(int argc, _TCHAR* argv[])
{

    SmartPtr<int,NoCheck> p1(nullptr);
    SmartPtr<int,EnforceNotNull> p = p1;//I'm trying here to convert NoCheck to    

   // EnforceNotNull but it works for me only if I use ctor, if I use conversion optor   
//(from  


  //  NoCheck to EnforceNotNull) it doesn't work why?
    return 0;
}

Answer 1

Your operator EnforceNotNull<T>() function is not const, so the compiler isn’t including it in the set of possible conversion functions. Uncomment EnforceNotNull copy ctor or put a const on the above function and your code should work.